Here is a UUID:
We made it with TapGuid a moment ago. Nobody has made this exact ID before, and nobody is likely to make it again, anywhere in the world.
TapGuid also gave it a color, a dusty purple (#846B9D). Ask a developer what color their UUIDs are and you'll probably get a puzzled look, because UUIDs don't have colors. In TapGuid, every one of them does, and we'd like to explain why. First, though, a word on what UUIDs are and why they don't repeat.
What is a UUID?
A UUID, short for universally unique identifier, is a label designed to be unique without anyone keeping a list. It's a very large number, 128 bits long, usually written as 32 letters and digits in five groups joined by hyphens, 36 characters in all. GUID, short for globally unique identifier, is Microsoft's name for the same thing. TapGuid is named after the GUID, but it makes exactly the same IDs.
Anyone can make a UUID on any device, even offline, without asking anyone first. Two phones on opposite sides of the world can each create millions of them, and their IDs won't clash. That's why so much software uses UUIDs to name things like photos, documents, orders, and devices.
You have probably met a few without noticing. Minecraft gives every player account a UUID, which is how you can change your player name and still be the same player. Windows uses GUIDs all over the system; the well-known "God Mode" trick is just a folder named with one, GodMode.{ED7BA470-8E54-465E-825C-99712043E01C}. Even Bluetooth devices use UUIDs to tell your phone what they can do, such as report a heart rate or a battery level.
Why UUIDs don't repeat
Most UUIDs today are version 4, which means they're random. Of their 128 bits, 122 are random, and the other six only mark what kind of UUID it is. That leaves about 5.3 undecillion possible UUIDs, a number with 37 digits.
A number that big is hard to picture, so try this instead. Imagine making a billion UUIDs every second. After about 86 years, there would be a 50% chance that two of them were the same. If you like the math, Wikipedia's article on UUIDs walks through it. So "unique" does come with small print: a repeat is possible, just so unlikely that in practice nobody plans for it.
One UUID, many ways to write it
The same UUID can be written in several formats, depending on where it goes. TapGuid shows each format on its own tab, ready to copy. Here is our purple UUID in five of them:
- Standard:
d203e949-b6f9-445a-b5fa-068afa94841f - Digits only:
d203e949b6f9445ab5fa068afa94841f - Braces, common on Windows:
{d203e949-b6f9-445a-b5fa-068afa94841f} - URN:
urn:uuid:d203e949-b6f9-445a-b5fa-068afa94841f - Base64, a shorter way to write the same 128 bits:
0gPpSbb5RFq1+gaK+pSEHw==
TapGuid also has parentheses and URL-safe Base64 formats, and can switch the letters to uppercase.
Why each UUID gets a color
Try comparing these two:
ad852fa5-173c-4772-88c4-5b342289d79d
ad852fa5-173c-4772-88c4-5b342289d79e
Only the last character is different, and most of us would miss it in 36 characters of look-alike letters and digits. Here are the same two, with the colors TapGuid gives them:
One is purple and the other a dusty rose. TapGuid calculates each color from the UUID's own characters, so the color works like a small visual fingerprint. When you tap for a new UUID, the whole screen changes color, and you know at once that you have a new one. The color also gives each ID a little personality. "The purple one" is easier to remember than ad852fa5.
The catch is that there are far fewer colors than UUIDs: about 2.1 million colors for 5.3 undecillion UUIDs. Many UUIDs have to share a color, and once you have made about 1,700 of them, there is already an even chance that two share one. So treat the color as a hint. Two different colors always mean two different UUIDs, but the same color doesn't prove that two UUIDs are the same. For that, you still have to compare the characters.
If you'd rather have a calmer screen, or need stronger contrast, you can switch TapGuid to its grayscale mode instead.
For the curious: how the color is made
The color comes from a few lines of code, which you can read in TapGuid's source on GitHub.
TapGuid first runs the UUID's text through FNV-1a, a small and fast hash function that turns any text into a 32-bit number. Change even one character and the number changes, and so does the color. TapGuid then takes 24 of those bits as a color, 8 each for red, green, and blue.
Raw colors from a hash can be harsh, anything from neon green to near black, so TapGuid mixes each one half and half with a medium gray, #666666. Every channel ends up between #33 and #B3. That keeps the shades muted, and black or white text reads comfortably on all of them; TapGuid picks whichever of the two has more contrast. The mix also narrows the range. Each channel has 129 possible values instead of 256, which makes 2,146,689 possible colors, the "about 2.1 million" from earlier.
TapGuid makes version 4 UUIDs by default, and its settings also offer versions 1, 6, 7, and 8. Version 7, added to the UUID standard (RFC 9562) in 2024, starts with a timestamp, so UUIDs made close together sort in order, which databases like. It also means they look alike at the start. These three were made about a second apart, and they share their first 13 characters:
Try TapGuid
TapGuid makes a new UUID with every tap, in the format you need, ready to copy or share. It runs in your browser on almost any device and installs like an app, and there is also a native Android version. It's free and open source, works offline, and has no ads and no extra permissions.
You can open TapGuid in your browser or get it on Google Play. What color is your next UUID?
